Automatic volume control with noise suppression



Oct. l, 1940. L. E. BARTON 2,216,582

AUTOMATIC VOLUME CONTRL WIT NOISE SUPPRESSION Filed NOV. 3, 1932 '3Sheets-Sheet 1 AUB/0 AMI? DE! VE E' ISIDETECTOE ott. 1, 1940. E EBA'RTQN 'I 2,216,582

AUTOIATIC VOLUME CONTROL WITH NOISE SUPPRESSION med Nov. s, 1932 :ssheets-sheet 2 ATTO/EWEK Oct. l, l940. l.. E. BARroN 2,215,582

I' AUTOHATIC VOLUME CONTROL WITH NOISE SUPPRESSION Filed NOV. 5) 1932 3Sheets-Sheet 3 INVENTOR Loy EBarvn,

Patented Oct. 1, 1940 UNITED STATES i l nessi AUTOMATC VOLUME CONTROLWITH N @ISE SUPPRESSION Loy E.- Barton, Collingswood, N. J., assigner toRadio Corporation of America, a corporation of Delaware ApplicationNovember 3, 1932, Serial No. 640,946

34 Claims.

My invention relates to signal receiving apparatus, and it hasparticular relation to devices for preventing the response of suchapparatus to signals of amplitude less than a predetermined value.

It has previously been proposed to provide signal receiving apparatuswith automatic volurne control devices whereby the ultimate sound outputis rendered substantially independent of fading and other phenomenawhich tend to cause the amplitude of an incoming signal to greatly vary.In the operation of receivers equipped with automatic volume controldevices, however, some dissatisfaction has been experienced by reason ofthe fact that, during the operation of manually or automatically tuningthe system from one desired station setting to another, interveningstations are received. Furthermore, during the tuning operation, thereis always present, from a wide variety of sources, objectionableinterference of the type generally designated as background noise.

It is, accordingly, an object of my present invention to provide meanswhereby a portion of l'. a radio receiver is rendered inoperative duringthe tuning operation.

Another object of my invention is to provide means whereby backgroundnoise shall be eliminated during the operation of tuning a signalreceiving system from one desired station to another station.

Ano-ther object of my invention is to provide, in a system of the typedescribed, means whereby automatic volume, or gain, control, as well assilent tuning, may be had without the necessity of using an extrathermionic tube.

A still further and more specific object of my invention is yto providea novel thermionic tube, through the use of which the foregoingenumerated functions may be had.

The aforementioned objects and other objects appurtenant thereto, Iprefer to accomplish through the use of a new and improved thermionictube wherein, in addition to the usual f triode structure, is disposedone, or more, diode plates providing, with the cathode of the tube,

additional space current paths. I also provide a system of resistors andpotential sources whereby the current traversing one, or more, of the:mj additional space current paths in the aforementioned tube gives riseto a potential, or potentials, proportional to the amplitude of anincoming carrier wave, and, in addition, I provide circuit connectionswhereby the said potential, or zijn potentials, may be utilized for bothvolume con- Ri l (Cl. Z50-20) trol purposes and-for the purpose ofrendering the system unresponsive to background noise or signals below apredetermined amplitude during the operation of tuning from one desiredstation i.

but it will hereinafter be noted that, irrespective of the specificnature of the triode portion of my improved thermionic tube, one of thediode elements is utilized for automatic volume control.

rIhe novel features that I consider characteristic of my invention areyset forth in particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages, will best beunderstood from the following descrip-tion of a specific embodiment andcertain variants thereof, when read in connection with the accompanyingdrawings wherein:

Fig. 1 is a diagrammatic view of a radio receiver of the superheterodynetype including a preferred embodiment of my invention,

Fig. 2 is a fragmentary diagrammatic view illustrating a modication ofmy invention,

Fig. 3 is a further fragmentary View of a radio receiver illustratingyet another modification of my invention,

Fig. 4 shows a modification of the circuit shown in Fig. 3.

Although, as will be obvious to those skilledv in the art, my inventionis applicable to radio receivers of many different types, I have foundit convenient to exemplify it in connection with a superheterodynereceiver. Referring specifically to Fig.. l of the drawings, asuperheterodyne radio receiver is shown including a preferred embodimentof my invention and comprises a radio frequency amplifier tube I of theradio frequency pentode type having a tunable input circuit 3 connectedto the control grid 5 thereof. A rst detector tube 1, of the same type,has its tunable input circuit 3 coupled to the output tunable circuit 5of tube I.

An intermediate frequency amplifier tube 9, also of the pentode type,follows the first detector; a combined second detector, automatic `gaincontrol, noise suppressor and audio frequency amplifier tube Il,constructed according to my invention, follows the tube 9. A driver tubei3 is coupled to the output of tube Il, and is followed by a pluralityof audio frequency amplifier tubes I5 and I1 connected in push pull, theoutput circuit of which may be coupled in any desired manner to aloudspeaker I 9 or other indicating device.

A local oscillator is included in the system, and is conventionallyindicated in the drawings by a rectangle 2. The oscillator is shown ashaving an output circuit 2 coupled to the input circuit 3 of the firstdetector tube l. Naturally, the oscillator in an actual receiverincludes a thermionic tube having a tunable resonant circuit which issimultaneously tunable with the tunable resonant circuits of the radioamplifier and rst detector stages of the receiver. In order to simplifythe drawing the specio connections of the said oscillator tube have beenomitted; the unicontrol tuning mechanism also being omitted for the samereason.

As is usual in receivers of the superheterodyne type, the couplingsbetween the radio freqeuncy amplifier I and the first detector 1,between the first detector and the intermediate frequency amplifier 9,as well as between the intermediate frequency amplifier and the seconddetector II, are of the band pass type. Such couplings are constitutedby radio frequency transformer M1 and intermediate frequencytransformers M2, and M3, respectively, each of the latter two having atunable primary and a tunable secondary winding. The transformers M2 and1W; are resonant to the operating intermediate frequency; the latter iskept constant in any desired manner throughout the tuning range of thereceiver.

The second detector tube may be coupled to the driver tube I3 in anydesired manner; I nd it expedient to utilize a coupling network sodesigned as to permit of compensated volume control. The network willhereinafter be referred to in more detail. As is customary in radioreceivers of the so-called "all electric type, the cathode heating, gridbiasing and anode potentials of the receiver tubes are supplied from acommercial alternating current supply line.

Specifically, the potential supply system I have found satisfactoryincludes a power transformer P having a plurality of secondary windingsS1, S2, S3, and S4. The windings S2, and S1, respectively, supplycathode and plate potential to a full wave rectifying device R, whilethe last mentioned windings S3 and S4 supply cathode heating potentialto the several tubes in the system. 'I'he rectifier R is provided withan output resistor, or potential dividing device R1, and in the negativeconnection thereof I find it expedient to dispose the field winding L1of the loud speaker of a sound producing device for a purpose which willlater be referred to.

Plate potential to all ofthe amplifying tubes in the system is suppliedfrom the positive end of the output resistor R1 over a common conductor6. Screen grid potential is supplied to the radio frequency amplifier I,the first detector T, and the intermediate frequency amplier 9 from anintermediate point a. on the output resistor R1 over a common conductor6. The multiple duty tube II comprises a cathode I2, a control grid II',an anode I4, and a plurality of diode anode elements I6 and I8.

As hereinbefore pointed out, it is one of the objects of my invention toprovide a receiver wherein tuning is silent. In order that this may beaccomplished, I utilize one of the diode elements as a detector, andsupply the said element with a controllable bias potential of suchmagnitude that incoming signals supplied thereto from the intermediatefrequency amplifier are not rectiiied unless the said signals exceed adefinite predetermined amplitude. The manner in which the controllablebias is supplied to the diode element is as follows: The cathode I2 ofthe tube II is connected to the most negative portion of the potentialsupply system through a cathode resistor 2U.

The grid Il of the said tube is connected through an adjustable contactdevice 2I to a point on a resistor 22 which, in turn, is shunted acrossbetween the said most negative portion of the potential supply systemand a point b on the output resistor R1 at a positive potential withrespect to ground. The path to the device 2| also includes the resistors23, 24. Adjusting the movable contact element 2| permits the grid I I'of the tube II to be supplied with a potential which is either positiveor negative with respect to the grounded point of the said outputresistor.

In the operation of the system, and assuming that no signals are beingimpressed upon the diode element I 6 of the tube I I, the movablecontact device 2I is adjusted along the resistor 22 until the fall inpotential along the self-bias resistor 2D is substantially balanced bythe rise in potential across the loud speaker eld winding L1, wherebythe grid II of the tube II and the diode element I6 are maintained atzero potential with respect to the cathode, or at a potential which isslightly negative. The amount of the negative potential is, of course,determined by the position of the contact element 2l, and adjustment ofthis element may be so made that the diode element does not functionuntil the said negative potential is overcome by an incoming signalhaving a definite predetermined amplitude. This feature enables thesystem to be adjusted for silent tuning.

Assuming now that the incoming signal eX- ceeds the predeterminedminimum amplitude, it is applied between the diode element I6 and thecathode I2 of tube II through grid leak resistor 24 and condenser 24.The control grid II of the tube is connected to the high potential sideof the grid leak 24 through resistor 23. It will be noted that theintermediate frequency voltage applied to the control grid will be verysmall, and that the resistor 23 is inserted to further reduce the signalat the intermediate frequency. It should also be apparent that the biasfor the control grid is obtained from the direct current voltage acrossthe grid leak 24 which, in turn, is proportional to the carrier of thesignal.

The plate current of the triode portion of the tube is limited by aresistance 25, (or a series combination of plate, reactor andresistance) in series with the plate supply conductor 6, and by thecathode resistor 20 so that the voltage across the said cathoderesistance is a maximum at zero signal and decreases as the signalincreases.

It will also be apparent that the voltage across the cathode resistance20 and the loud speaker eld L1 are in the same direction, and thatnormally the voltage across the said resistor 20 is larger than thevoltage across the eld in the absence of signals. In this condition,therefore, the diode plate I6 may be negative with respect tothe cathodeof the tube depending upon the adjustment of resistance 22. 'Ihe seconddiode plate I8 is negative in the last named condition,

and is connected over a conductor 26 and a plurality of resistors 21,28, 29 to ground.

In the no signal condition the potential drop across the cathoderesistor 20 is greater than the rise in potential across the lo-udspeaker field L1 and, accordingly, a negative potential is supplied tothe said secon-d diode element I8. For automatic volume controlpurposes, the grids of the radio frequency amplifier I, the firstdetector 'I and the intermediate frequency amplifier S are connected toappropriate points on the aforesaid resistors included between thesecond diode plate I8 and ground. Thus, the grid of tube I is connectedto one side of resistor 28; the grids of tubes 1, II are connecte-dthrough lead 30 to a point intermediate resistors 28, 29. This permitsthe bias applied to the grid of tube I to be greater than that appliedto tubes 'I and 9 to prevent overloading on the side of a strongcarrier. Obviously, therefore, during the no signal condition thenegative bias applied to the said tubes is a minimum, and is determinedsolely by the potential drop across the self-bias resistor 3| connectedinto the cathode return circuit of tubes I and 9.

As a signal is applied to the diode plate I6 its rectification causes anegative potential to be developed across the grid leak 24, and, sincethe control grid II' of the tube is connected to the said grid leak ashereinbefore explained, it becomes more negative, thus causing the platecurrent of the triode section of the tube II to decrease. The decreasein current through the cathode resistor 20 permits the second diodeelement I8 to become more positive With respect to cathode l2 by theamount of change in the difference of the voltage across the loudspeakerfield and the cathode resistor 20. If the input signal is sufficientlylarge, the decreased voltage across resistor 20 causes the diode anodeI8 to become positive with respect to cathode I2 by virtue of the factthat cathode v I2 becomes negative with respect to ground, Therefore,current ows from ground to the diode anode I8 through resistors 29, 28and 21, the voltage across these resistors being essentially equal toground and the potential of cathode I2 because the resistance of thediode anode I8 is relatively small. The direction of this current isfrom ground up through the resistors 29, 28, 21, included between groundand the diode plate, causing a potential drop in the proper direction tosupply bias to the radio frequency amplifier I, the rst detector 1, andthe intermediate frequency amplier 9 for automatic volume controlpurposes. Obviously, the amount of current taken by the second diodeelement I8 increases as the signal increases in amplitude, and thus theincreased signal is caused to be met by tubes the gain in which has beendecreased.

In general, the voltage across the cathode resistor 2! during the nosignal condition should be about 30 to 50 volts higher than the voltageacross the loud speaker winding. This voltage determines the extent towhich the automatic volume control action is delayed. The signal appliedto the first diode element I5 may cause a reduction in voltage in thesaid cathode resistor 20 to approximately 60% of the initial voltagewithout serious distortion of the audio signal. In this connection,attention is called to the fact that there will be no automatic volumecontrol until the voltage across the cathode resistor 20` isapproximately equal to the voltage across the loud speaker field, sothat a voltage for automatic volume control of 60 to '15 volts may beobtained without overloading the detector I I, if the voltage across theloud speaker field is about 1'10 volts and the plate supply for thereceiver is about 230 volts.

The maximum voltage available for automatic volume control depends uponthe available voltage across the speaker and resistor 20. Referringagain to the action of the second detector tube l I, it should be notedthat the audio voltage, due to the rectification of the signal by therst diode element IB, is applied to the control grid II', whereby thesaid tube functions not only as a detector, but also as an audiofrequency amplier. The noise suppression, or silent tuning, is obtainedby adjustment of the contact device 2I associated with the resistor 22which shunts a portion of the rectifier output resistor R1 and the loudspeaker field winding. Naturally, if the contact element is moveddownward toward the negative end of the shunting resistor, a signal ofgreater amplitude or noise of greater amplitude is required to overcomethe negative bias applied toV the first diode element I6. In locationswhere interstation noise is not objectionable, the diode plate I6 may bemaintained at substantially zero potential by proper adjustment of thecontact element. It should be .noted that if the diode anode I5 is madenegative with respect to the cathode by the adjustable tap 2 I, a signalslightly larger than this value is required to overcome the bias tocause some detection. The negative. potential to grid Il increases dueto detection which automatically reduces the cathode potentialwithrespect to the point 2 I, thereby removing the negative potential onthe diode anode I6 and thus permitting normal detection.

In order that a further control of the sensitivity of the system may behad, I prefer to supply normal bias to the radio frequency amplier andthe intermediate frequency amplifier through a variable self-biasresistor 3l which is connected by leads 32, 33 between the cathodes ofthe said tubes and ground. Through proper adjusting of the said variableresistor, since in the no signal condition no bias is supplied from thecircuit of the second diode plate I8, the normal bias on the said tubesmay be adjusted to the desired point. l

The resistor 25 is by-passed with the condenser 311, and the audiovoltage is obtained from the resistor 25 (and/or choke) in the platecircuit of tube Il through resistor 35 and condenser 36 to thepotentiometer 31. The network, including the series condenser-resistorpaths X, Y, Z, associated with the potentiometer 31, or the audio volumecontrol, are used to obtain the desired compensation for varying volumelevels and also tone control. 39 are used as a hum filter, if such isnecessary. The network between tubes II and I3 need not be described inany further detail, since it is not a part of they present invention.The .amplier tubes I5 and I1 are arranged in push-pull, and need only bedescribed as furnishing an amplifier of the class B push-pull typeoperating with zero grid bias. This arrangement has been described andclaimed by me in a co-pending application Serial No. 586,874, filedJanuary 15, 1932, granted June 15, 1937 as U. S. Pat. 2,084,180,

and is also described in the I. R. E. for July,

The tube I I is of the type known as an RCA-55, or a duplex-diodetriode. The diode elements I6, I8 are disposed around an extreme portionof the cathode sleeve. vThe cathode is common for The resistor 38 andcondenser the diode elements and the triode grid and plate. However, thediode anodes I6, I8 function independently of the triode elements. Thatis, the diode anodes I6 and I 8 are outside the electron system betweencathode I2, grid II and anode I4. Further details of the construction ofthis tube will be found in a co-pending application of T. M. Shi-aderapplication Serial No. 622,140, filed July 12, 1932, granted Oct. 27,1936 as U. S. Pat. 2,058,834.

In Fig. 2 there is'shown a modied form of the automatic volume controland noise suppressor arrangement of Fig 1. The combined second detector,automatic volume control, noise Suppressor tube is designated by thenumeral 40. This tube is of the co-planar grid type with a diode anode,indicated as D1.

The grid 4I is connected to the one side of the tuned secondary windingof the transformer M3, in the same manner as the diode element I6 in thecase of tube II of Fig. 1. The grid 4I is connected to the other grid4I, and to the potentiometer R1 through a path which includes resistor43 having a value of about 2 megohms, and a resistor 44 having amagnitude of about 20,000 ohms, a condenser 45 being connected betweenthe junction of resistors 43 and 44 and the cathode of tube 40. Itshould be noted that the resistor 43 may be connected to the center ofthe secondary of coupling transformer M3 without altering the operationof the grids.

The cathode of tube'llll is connected to the -B side of a power supplysystem through a resistor 46 which functions in the same manner asresistor 20 in Fig. 1. The main anode 47 of tube 40 is connected to the+B side of a power supply system through a network 48, tuned to thesecond harmonic, the primary winding 49 of the audio frequency couplingtransformer M4, and lead 50. The condenser 5I connects the low potentialside of the winding 49 to the cathode of tube 40. The tuned circuit 48increases the sensitivity of the tube 40 slightly but may be omitted.

The preceding intermediate frequency amplifier tube 9 has its cathodeconnected to the -B side of the power supply system through a path whichincludes the resistor 52, and the loud speaker eld winding 53, thejunction of resistor 52 and field winding 53 being connected to the lowpotential side of the tuned input circuit of tube 9 through agroundedresistor 54 having a value of about 0.5 megohm. The resistor 55 is'connected between the junction of resistor 52 and the winding 53 and theanode lead to tube 9, one side of the potentiometer resistor R1 beingconnected to an intermediate point of the resistor 55. The diode anodeD1 of tube 40 is connected to the low potential side of the grid circuitof tube 9 through a path, which includes lead 56 and resistor 51 inorder to cause resistor 54 to feed automatic volume control voltage totube 9.

The co-planar grid tube 40 is a tube wherein the grids 4I and 42 areconcentrically wound in the same cylindrical surface. The diode anode D1is disposed outside the main electron stream from the cathode to theanode 41, and therefore provides a diode independent of the co-planargrid triode. The circuit of diode anode D1 provides delayed automaticvolume control action. Potentiometer R1 is so adjusted that in theabsence of signals the grid-cathode bias is zero. The voltage across theresistor 46 decreases with signal because of the negative potentialacross 43 which is proportional to the signal and, until this voltagedecreases to a certain predetermined value, say 160 volts from 190volts, the bias for the intermediate frequency tube 9 will be normal.When such predetermined voltage has been reached, current begins to owthrough the resistor 54 due to the potential across resistor 46 havingbecome less than that across eld winding 53 so that anode D1 has becomepositive relative to the cathode of tube 40. Further increase in signalcauses a decrease in voltage at resistor 46, and this increases the biason tube 9. The arrangement shown in Fig. 2, also, includes noisesuppression so that most, or all, noise when tuning between stations isautomatically suppressed. The potentiometer R1 can be so adjusted thatthe tube 40 will have a negative bias on the grids 4I and 42, therebypreventing detection until a carrier of a predetermined amplitude isreceived. Signal detection causes the voltage across 46 to decrease, tosay 160 volts, which removes the negative bias so that the grids 4I and42 may detect in a normal manner. Further decrease in voltage across 46automatically controls the sensitivity of the receiver by applying thefurther decrease as bias to the tube 9 through circuit 54, 51, 56 andthe diode D1. Ihe grids 4I and 42 will become positive but the actualpositive potential will be very small because of the high resistance 43.The slight positive potential will not interfere with detection.

In Fig. 3 there is shown a modification of the automatic volumelcontrol, delay and noise suppressor circuits of tube II in Fig. 1. The55 type tube II is used for the second detector, automatic volumecontrol and noise suppression functions, as in the case of Fig. 1.Referring to Fig. 3, the input intermediate frequencyk signal is appliedto the diode anode D1 with the condenser and leak arrangement C1-R4.Contacts S1 are insulated from the contact arm S2 but are somechanically connected that the contacts are closed when Sz is atextreme right. It will be noted that when the sensitivity control S2 isat the extreme right hand position, the sensitivity is maximum, and theswitch contacts S1 are caused to be connected together by the movablearm Sz, so that the diode element D1 returns directly to the indirectlyheated cathode sleeve. The tube II in Fig, 3 has been shown in greaterconstructional detail than in the case of Fig. 1 so as to show thepositioning of the control grid and main anode, as well as thepositioning of the auxiliary anodes D'1 and D2 with respect to thecommon cathode sleeve I2'.

When the arm S2 is in the extreme right the controlling shaft will alsocause the switch contacts S1 to be closed as described above, and thebias on the element D1 is zero as well as on the grid II if the inputsignal is zero. The plate current for the tube I I ows through resistorR1, and returns to the negative plate potential through resistor R2which is in the cathode lead of tube II. The voltage drop acrossresistor R2 is somewhat higher than the voltage across the loud speakercoil L3. The resistor R1 is used as a plate coupling resistor for theaudio signal, and the condenser C5 by-passes the audio signal aroundresistor R2, and also lters out any hum that may exist in the platesupply to tube II.

Under no signal conditons, and with the arm S2 in extreme right positionso that the two contacts S1 are closed, there is a negative potential onthe diode element D2 through the biasing resistor R10. Therefore, thereis no current flowing through the resistor R1o, so that the bias on theradio frequency and intermediate frequency systems is the minimum orfixed value. As a signal is applied to the element D1, the rectiiicationcauses a negative potential to be generated across resistor R4, and thisin turn causes the plate current of the triode section of tube II todecrease. This decrease in current through resistor R2 results in alower voltage drop across the latter, so that as the signal increases,the voltage across resistor R2 will become less than the voltage acrossthe speaker iield winding L3. Under these conditions, the diode elementD2 will become positive by the amount of the difference in voltageacross resistor R2 and the iield I provided here, with regard to thedelay action, a

rectifier system for producing audio and direct current components fromthe signal energy, a triode amplifier for amplifying both components,and an additional device of asymmetric conductivity for utilizing theamplified direct current component for delaying the automatic volumecontrol action until the signal energy rises above a predeterminedthreshold value.

In general, the voltage across resistor R2, with no signal, should beabout to 50 volts higher than the voltage across the winding L3. Thesignal applied to the diode element D1 may cause a reduction in thevoltage across resistor R2 to approximately 60% of the initial voltagewithout serious distortion of the audio signal. It Will be noted thatthere will be no automatic volume control action until the voltageacross resistor R2 is approximately the voltage across the winding L3 sothat a net voltage for automatic volume control of 60 to '75 voltsshould be obtained without overloading the detector tube II. The audiovoltage due to modulation will be applied to the grid II' through theresistor R5, and will be transmitted to the audio system through theplate resistor Ri and the coupling capacitor Cs. The resistor Re is usedto reduce the intermediate frequency energy to the grid II, but will notaffect the audio frequencies appreciably.

The effective circuit which resultswhen the arm S2 is in contact withcontacts S1 may be had by referring to Fig. 4. This circuit will be thesame as Fig. 3, except that the switch contacts Si, the leads connectingSi, the resistor R5, and the .condenser C2 should be omitted from thecircuit. The low potential end of R4 will connect to the cathode of tubeII to complete the changed circuit.

The noise suppression function is obtained by adjusting thepotentiometer Ra slightly to the left, which opens the switch S1. Inother words, when the arm S2 is moved to the left along thepotentiometer resistor Rs, the two contacts of switch S1 are open, ordisconnected, and the noise suppression function is restored. With thissetting, that is the arm S2 moved slightly to negative potential amountsto approximately 8 volts, so that an incoming signal below this valuewill not be detected. Therefore, no noise will appear at the loudspeaker.

If the noise level is such as to over-ride the suppressor, or negativediode, potential, then sensitivity may be reduced (by moving the arm S2still further to the left) by increasing the normal negative bias on thegrids of the control tubes thus making the overall amplication less sothat the noise will not over-ride the negative potential on the diodeelement D'1. If this procedure is carried far enough it is obvious thatno station .can be received, so that the range of the sensitivitycontrol should be limited to such a value that stations with high eldstrength can be received at the minimum sensitivity. This latter minimumpoint of sensitivity will then represent the extreme left position ofthe arm S2 on the potentiometer resistor Rs.

The principal advantages of the system shown in Fig. 3, as well as thatshown in Fig. 1, reside in the fact that the detector, delayed automaticvolume control and noise control functions are performed by only onetube. The audio output of the detector is approximately 50 volts formodulation before it overloads if the necessary intermediate frequencyvoltage is applied to the detector. This relatively high audio voltagepermits the use of a compensated volume .control. The voltage for theautomatic volume control is also more dependable because it depends upona change in plate current of the detector and does not depend directlyupon power from the intermediate frequency system. n

The noise control'feature providesa means for using a sensitivitycontrol with a negative potential on the diode detector. potential onthe diode eliminates the noise applied to the detector below a definitevoltage, and the sensitivityv control permits an adjustment of noiselevel to the detector. An ordinary, sensitivity control in somereceivers can be used as a volume control, but in the above system anadjustment of the sensitivity control either causes the'signal todisappear or to be receivednor` mally with a very limited range in whichthe signal is badly distorted. The result is that the user would notattempt to use the noiseplevel or sensitivity control as a volumecontrol.

The circuit shown in Fig. 3 normally supplies audio Voltage through thecoupling capacitor C6 to a high resistance potentiometer arrangement forcompensated volume control, which potentiometer may be connecteddirectly to the grid of an audio frequency driver tube. This lattervolume control arrangement is shown in Fig. 1 between the tubes II andI3. rIThis is a satisfactory arrangement when the load in the platecircuit of the tube I I is very light, or has a high resistance.However, it is desirable at times to connect a transformer M6 to theplate circuit of the detector tube II sothat a push-pull output system,of the type shown in Fig. 1 bytubes I5 and I'I, .can be driven directly.In general, the latter arrangement means a relatively low resistance inthe plate circuit of tube II so that it is not desirable to `use theresistance-condenser coupling network shown in Fig. 3.

The circuit arrangement shown in Fig. 4is designed to eliminate theplate load difliculty referred to in the preceding paragraph, and yetretain most of the desirable features of the circuit shown in Fig. 3.vThe principal feature of the modification in Fig. 4 is the relativelylow leak resistance R4, having a value of 0.1 megohm,

The negative lis to'y

with the high resistance audio volumecontrol P2, the resistor R of themanual volume control P2 having a value of about 1 megohm. The functionof the manual volume control is similar to the compensated volumecontrol in Fig. 1. It will be noted that the bias for the triode actionof tube Il is the voltage across the resistor R4 so that the system forautomatic volume control, detection and noise control as used in Fig. 3may be employed here also. The resistor Re may be omitted if desired.

While I have indicated and described several systems for carrying myinvention into eiiect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention as set forth in the appendedclaims.

What I claim is:

1. In combination, with a high frequency amplier whose gain is to becontrolled in such a manner that the output of the amplifier ismaintained at a substantially uniform level, a rectifier including asource of electrons and a cold electrode coupled to the amplifieroutput, means connected to the cold electrode of the rectier formaintaining the cold electrode negative with respect to the source ofelectrons when signals to be amplified are impressed upon the controlledamplifier input, an amplifier including a source of electrons and atleast two cold electrodes, one of the two cold electrodes beingconnected to a point on said means, and the other cold electrode beingconnected to the source of electrons of the amplifier, a delay spacedischarge device electrically connected to the source of electrons ofsaid amplifier, and an automatic volume control resistor connectedbetween a cold electrode of the delay device and the high frequencyamplifier.

2. In combination, an amplifier to be controlled as to the gain thereof,a rectifier, a second amplifier, means for impressing the rectifieroutput upon the second amplifier input, a device of asymmetricconductivity, means for impressing the second amplifier ouput on saiddevice whereby the output of the second amplifier produces negligibleeffect in the output of said device until a desired threshold value isattained, and a direct current voltage connection between the output ofsaid device and said controlled amplifier, the gain of said controlledamplifier being controlled from said device only after said thresholdvalue is reached.

3. In combination, an amplifier to be controlled as to the gain thereof,a rectifier, a second amplifier, means for impressing the rectifieroutput upon the second amplifier input, a diode device, means forimpressing the second `amplifier output on said device whereby theoutput of the second amplifier produces negligible effect in the outputof said device until a desired threshold value is attained, and a directcurrent voltage connection between the output of said device and saidcontrolled amplifier, the gain of said controlled amplifier beingcontrolled from said device only after said threshold value is reached.

4. In combination, an amplifier to be controlled as to the gain thereof,a rectifier, a second amplifier, means for impressing the rectifieroutput upon the second amplifier input, a device of asymmetricconductivity, means for impressing the second amplifier output on saiddevice whereby the output of the second amplifier produces negligibleeffect in the output of said device until a desired threshold value isattained, and a direct current voltage connection between the output ofsaid device and said controlled amplifier, the gain of said controlledamplifier being controlled from said device only after said thresholdvalue is reached, said second ampli; fier comprising an electrondischarge tube including a cathode, control grid and anode, and saiddevice consisting of an auxiliary anode disposed adjacent said cathodeoutside the electron stream between the cathode and the first saidanode.

5. In combination, an amplifier to be controlled as to the gain thereof,a rectifier, a second amplifier, means for impressing the rectifieroutput upon the second amplifier input, a device of asymmetricconductivity, means for impressing the second amplifier output on saiddevice whereby the output of the second amplifier produces negligibleeffect in the output of said device until a desired threshold value isattained, and a direct current voltage connection between the output ofsaid device and said controlled amplifier', the gain of said controlledamplifier being controlled from said device only after said thresholdvalue is reached, said second amplifier comprising an electron dischargetube including a cathode, control grid and anode, and said deviceconsisting of an auxiliary anode disposed adjacent said cathode outsidethe electron stream between the cathode and the first said anode andsaid rectifier' comprising an additional auxiliary anode disposedadjacent said cathode outside said electron stream.

6. An automatic volume control arrangement for a radio receiver, whichreceiver includes a high frequency amplifier and a detector, saiddetector' including an electron discharge tube provided with a cathode,at least one control grid and at least one anode, a resistor in thecathode circuit of said detector tube, at least one auxiliary coldelectrode in said detector tube, a direct current voltage connectionbetween said auxiliary electrode and said amplifier for controlling the`gain of the latter, the voltage across said cathode resistor being of amagnitude exceeding the bias requirement for the detector.

7. An automatic volume control arrangement for a radio receiver, whichreceiver includes a high frequency amplifier and a detector, saiddetector including an electron discharge tube provided with a cathode,at least one control grid and at least one anode, a resistor in thecathode circuit of said detector tube, at least one auxiliary coldelectrode in said detector tube, a direct current voltage connectionbetween said auxiliary electrode and said amplifier for controlling thegain of the latter, the voltage across said cathode resistor being of amagnitude eX- ceeding the bias requirement for the detector, a secondauxiliary cold electrode Within said detector tube, said secondauxiliary electrode being connected to the output of said amplifierwhereby it cooperates with a portion of said detector tube cathode torectify signals supplied to the detector, means for connecting saidcontrol grid to a point on the detector input circuit whereby a widerange of voltage variation across said cathode resistor is secured.

8. An automatic volume control arrangement for a radio receiver, whichreceiver includes a high frequency amplifier and a detector, saiddetector including an electron discharge tube provided With a cathode,at least one control grid and at least one anode, a resistorin'thecathode circuit 0f said vdetector tube, at least one auxiliary coldelectrode in said detector tube, a direct current voltage connectionbetween said auxiliary electrode and said amplifier for controlling thegain of the latter, the voltage across said cathode resistor being of amagnitude eX- ceeding the bias requirement forI the detector and anadditional control grid coplanarly arranged with respect to the rstcontrol grid connected to a signal potential point on the detector inputcircuit which is out of phase with the point on the said input circuitto which the said first grid is connected.

9. In combination with ahigh frequency amplier stage whose gain is to becontrolled, a tube provided with at least a cathode, control grid, andanode, and a pair of .auxiliary anodes positioned outside the electronstream between the cathode and said anode, a signal input circuitcoupled between one of said auxiliary elecitrodes and the cathode, saidsignal input circuit being additionally coupled to the output of saidamplifier, means for coupling said tube anode to a low frequencyamplier', a direct current voltage connection between said control gridand said one auxiliary electrode, a direct current voltage connectionbetween the other auxiliary electrode and said first amplifier, aresistive path in the cathode circuit of said tube, and an adjustableconnection between said direct current voltage connection to said secondauxiliary electrode and said resistive path.

10. In a superheterodyne radio receiver including an intermediatefrequency amplifier, a second detector tube including a triode sectionand at least one independent diode section, an audio amplifier networkconnected tothe output electrodes of the triode section, a signal inputcircuit connected to the diode section to provide a rectication network,and a biasing impedance in the cathode circuit of the triode sectionconnected to the said diode section for rendering the latter inoperativewhen signals of less than a predetermined amplitude are impressed onsaid input circuit, an auxiliary electrode in said tube pro- 7 providedwith a cathode, a grid, an anode, and at viding a second independentdiode section, and a direct current voltage connection between theauxiliary electrode and a gain control electrode of the intermediatefrequency ampliiier.

ll'. In a superheterodyne radio receiver .including an intermediatefrequency amplifier, a second detector tube including a triode sectionand at least one independent diode section, an audio amplifier networkconnected to the output electrodes of the triode section, a signal inputcircuit operative when signals of less than a predetermined amplitudeare impressed on said input circuit, an adjustable audio volumeconnection between the grid of said triode section and apoint on saidrectication network, and additional means for frequency compensating thesaid connection for different volume levels.

12. In a receiver of the type including at least one high frequencyamplifier having a resonant input circuit, a detector stage including atube least two cold electrodes adjacent said cathode but substantiallyunaffected by said grid, a signal circuit coupled to one of the coldelectrodes and the cathode to produce rectified signal cur-v to theamplifier, a connection from the cathode to a point more negative thanground, and a resistance in said connection which is traversed by theanode current whereby the potential of cathode with respect to ground ispositive in the absence of signals but becomes negative in the presenceof strong signals.

13. In a receiver of the type including at least one high frequencyamplier having a resonant input circuit, a detector stage including atube provided with a cathode, a grid, an anode, and at least two coldelectrodes adjacent said cathode but substantially unaffected by saidgrid, a signal circuit coupled to one of the cold electrodes and thecathode to produce rectified signal current, an impedance'which is highfor both direct and audio currents connected between said one electrodeand cathode to be traversed by said rectified signal current, means toimpress between the grid and cathode voltage derived from said rectifiedcurrent flowing through said impedance whereby the direct currentcomponent is decreased in proportion lto increasing signals, a directconnection from the other cold electrode to the amplifier, a connectionfrom the cathode to a point more negative th-an ground, and a resistancein saidr connection which is traversed by the anode current whereby thepotential of cathode with respect to ground is positive in the absenceof signals but becomes negative in the presence of strong signals,means. for selecting at will a desired potential difference between therectifier cold electrode and the cathode.

14. In combination with an amplier, rectier means for deriving a directcurrent proportional to an incoming signal, a space current deviceincluding an anode and a cathode, means for normallymaintaining saidanode negative with respect to said cathode, and means whereby the saiddirect current is' utilized to cause a reversal of the polarity of saidelectrodes, with consequent flow of space current.

15. In a receiver of the type including at least one high frequencyamplier having a resonant input circuit, a detector stage including a.tube provided with a cathode, a grid, an anode, and at least two coldelectrodes adjacent said cathode bult substantially unaiected by saidgrid, a signal circuit coupled to one of the cold electrodes and thecathode to produce rectified signal current, an impedance which is highfor both direct andV audio currents connecte-d between said oneelectrode and cathode to be traversed by said rectified signal current,means to impress between the grid and cathode voltage derived fromsistance in said connection which is traversed by` thel anode currentwhereby the potential of cathode` with respect to ground is positive inthe absence of signals but becomes negative in the presenceof strong'signals and means for biasing the second cold electrode more negativethan ground by an adjustable amount whereby current will not flow fromthe cathode to the second electrode until the cathode is more negative.

16. In a radio receiver, a radio frequency amplifier, a multiplefunction tube including a diode signal rectifier and an amplifier,circuit elements connecting said rectifier between said radio amplierand said second amplifier, means including a second diode forcontrolling the gain of said radio amplifier, and means forautomatically suppressing the transmission of rectified signals by saidtube when the radio frequency voltage impressed on said rectifier fallsbelow a predetermined value. i

17. In a radio receiver, a radio frequency ampliiier, a multiplefunction tube including a diode signal rectifier and -an amplifier,circuit elements connecting said rectifier between said radio amplifierand said second amplier, means including a second diode disposed in saidtube for controlling the gain of said radio amplifier, and means forautomatically suppressing the transmission of rectified signals by saidtube when the radio frequency voltage impressed on said rectifier fallsbelow a predetermined value.

18. A multiple duty tube including an evacuated envelope, a cathode, amain anode, and a pair of co-planarly wound grids disposed within theenvelope, said grids being arranged within the electron stream betweenthe cathode and anode, and an auxiliary anode, of a relatively smallerarea than said main anode, disposed adjacent said cathode outside saidstream, the electron stream between said cathode and auxiliary anodebeing unobstructed by any electrode and independent of the said firststream, means for connecting the auxiliary anode and cathode to providea diode rectifier circuit, and additional means for connecting the saidgrids to opposite sides of a signal input circuit.

19. In a radio receiver provided with a tube having a diode section andan electronic section including at least two cold electrodes and thecathode of said diode section, a signal input circuit connected to saiddiode section and providing a rectification network, a source of signalenergy, means for connecting one of said cold electrodes to a point ofalternating current potential in said network, and an auxiliary coldelectrode disposed adjacent said cathode providing a second diodesection, and a gain control connection between the auxiliary electrodeand said signal source.

20. In a radio receiver, the combination with a tube having an anode, acontrol grid, plate and cathode, of a radio frequency amplifier, meanscooperating with said anode and cathode to form a diode detector workingout of said amplifier, means for automatically controlling the gain ofsaid radio frequency amplifier, circuit elements for impressing uponsaid control grid an audio frequency Voltage developed by said diodedetector, an audio frequency load in the plate circuit of said tube,means establishing a bias voltage between cathode and another tube element to suppress the transmission of audio frequency currents by saidtube, and means operable automatically when the received radio frequencyvoltage rises above a critical level to reduce the bias voltage topermit normal transmission by said tube.

21. The invention as set forth in claim 20, wherein said means forautomatically controlling the gain of said amplifier includes a secondanode within said tube and cooperating with said cathode to form a dioderectifier.

22. In combination with an amplifier of modulated high frequency carrierenergy, a detector system comprising an electron discharge tube providedwith a cathode, a plate and at least one control grid disposed in theelectron stream between the cathode and plate, a resonant input circuitconnected between the grid and cathode, at least two resistors connectedin series with each other and connecting the grid and cathode. one ofsaid resistors nearest the cathode being disposed in the space currentpath of the tube for developing a detection suppression bias for saidgrid in the absence of carrier energy above a predetermined intensitylevel, the said grid having impressed thereon direct current voltagedeveloped across said other resistor when said energy increases abovesaid level whereby the space current fiow through the said one resistoris reduced.

23. A radio receiver comprising an amplifier with potentially operatedgain control means, a detector-amplifier-governor comprising a cathode,an anode, a grid and two auxiliary anodes arranged to receive electronsfrom the cathode without interaction with electrons fiowing to the otherelectrodes, a signal rectifier circuit comprising the cathode and anauxiliary anode coupled to an output circuit of the amplifier and to thegrid, and an automatic gain control circuit comprising a potentialsource, the cathode, the second auxiliary anode and a connection to thegain control means and a manually operated sensitivity control for saidfirst named amplifier.

24. In combination, a source of potential, a radio frequency amplifierwith potentially operative gain control means, an electron tube having ahot cathode and a plurality of cold electrodes arranged to receiveelectrons from the cathode without interaction with electrons flowing tothe other electrodes, a rectifier circuit comprising the cathode and acold electrode electronically related to the cathode only coupled to anoutput point in the amplifier, an amplifier circuit comprising thesource of potential, the cathode and cold electrodes coupled to therectifier circuit and an automatic gain control circuit comprising thesource of potential, an impedance, the cathode, a cold electrodeelectronically related to the cathode only and the gain control means.

25. In combination in carrier wave receiving apparatus, a source ofelectrical energy with potential taps, a carrier frequency amplifierwith manual and automatic gain control means, an electron tube having anamplifier section and two diode sections, a rectifier circuit includingone diode section coupled to the output of the carrier frequencyamplifier, an amplifier circuit including the amplifier section coupledto the rectifier circuit and energized from taps on the source ofenergy, and an auttomatic volume control circuit including the otherdiode section, a connection including an impedance from said diode to anintermediate tap on the source of potential, and a connection from thediode to the automatic gain control means in the carrier frequencyamplifier.

26. The method of carrier wave reception which comprises the successiveoperations of amplifying the carrier, rectifying the amplified carrier,re-amplifying the rectified carrier, bal ancing a direct currentcomponent of the reamplified rectified carrier against a fixed directcurrent and permitting current to flow for con-y all trollingamplification when the relative levels and polarities of the balancedcurrents satisfy predetermined conditions.

27. The method of governing the gain of an amplifier which comprisesrectifying the output of the amplifier, amplifying the rectified output,balancing the amplified rectified output against a steady current, andpassing governing current to control the gain of the amplifier when theamplified rectified output reaches a predermined level relative to thesteady current.

28. In combination with a diode rectifier circuit having a tuned inputcircuit, a load resistor in circuit with said tuned circuit between thediode anode and cathode, an electron discharge tube having at least acathode, plate and control grid, connections from the control grid andcathode of the tube to points of different direct current potentials onsaid resistor, the grid connection point being negative with respect tothe cathode connection, a network in shunt with said load resistorcomprising a resistor` and an audio by-pass condenser in series, andsaid control grid connection including an adjustable tap in slidingcontact with said series resistor whereby the impression on the grid ofthe audio component of the voltage developed across the load resistormay be varied without changing the said direct current potentialdifference between said grid and cathode.

29. In a radio receiver, the combination with a radio amplifier, adetector, a direct current amplifier working out of said detector, andhaving a plate-cathode resistance by-passed for radio frequencies, adiode having said resistance connected between the cathode thereof andthe anode through a serially connected resistor and a direct currentsource, said source impressing a positive potential upon said anode, anda circuit connection for impressing the direct current potential of oneof said diode elements upon said radio amplifier as a gain control bias.

30. A radio receiver as set forth in the above claim 29 wherein saiddestroyer, direct current amplifier and diode comprise elements within asingle vacuum tube.

3l. In the operation of a radio receiver including a radio amplifierworking into a rectifying system which produces a direct current voltagethat varies inversely with the radio input to the receiver, a device ofuni-lateral conductivity having an output resistance included in a gaincontrol circuit of said amplifier, and a source of direct currentpotential, the method o maintaining normal gain of said amplifier forall radio input below a critical value and then varying the gain withchanges in receiver input above that critical value which comprisesimpressing the output voltage of said rectifying system on said devicein a sense opposing conduction therethrough, and impressing upon saiddevice from said source a direct current voltage tending to produceconduction and of a magnitude neutralizing the blocking eect of saidfirst impressed voltage when the latter falls to the value correspondingto the said critical radio input to the receiver.

32. A radio receiver comprising an amplifier with amplification controlmeans, an electron tube having a cathode, anode, control grid and atleast two auxiliary anodes arranged to receive electrons from thecathode without influencing or being influenced by other electrodes, arectifier circuit embodying the cathode and an auX- iliary anode forrectifying signals and a uni-laterally conducting circuit embodying thecathode, a potential source and an auxiliary anode for automaticallycontrolling amplification for signals above a determined level.

33. In combination, a detector-governor comprising a cathode, anamplifier section and two auxiliary anodes, a rectifier circuitcomprising the cathode and one auxiliary anode, a governor circuitcomprising the cathode and second auxiliary anode and an amplifiercircuit comprising the cathode and amplifier section.

34. In a modulated carrier-current signaling system employing acarrier-current amplifier and rectifier, which rectifier produces amodulated uni-directional voltage, a direct current voltage connectionfrom said rectifier to an element of said amplifier whereby theamplification is automatically regulated, said connection including aspace discharge device of unidirectional conductivity, and a connectionfrom said rectifier to a modulation current amplifier whereby the signalis further amplified, and an additional connection from the output ofthe modulation current amplifier to the output electrode of saidrectifier for varying the potential of said rectifier output electrodein dependence on the intensity of received carrier current.

LOY E. BARTGN.

